1. Field of the Invention
The present invention relates to improvements in a wire electrical discharge machine, and more particularly to a wire electrical discharge machine which prevents a fluid from coming into contact with a capstan roller and a pinch roller, and in which a wire electrode is difficult to become intangled with the rollers.
2. Description of the Related Art
A conventional wire electrical discharge machine will be described with reference to FIGS. 6 to 7 disclosed in JP-A-4-105822. In FIGS. 6 and 7, the wire electrical discharge machine is a machine tool wherein a phenomenon of electric discharge is caused to take place between a wire electrode 1 and a workpiece 3 to perform cutting-out processing with respect to the workpiece 3 such as a superalloy. At the time of starting discharge machining, the wire electrode 1 must be inserted in advance in a start hole formed in the workpiece 3, and the wire electrode 1 must always be fed during wire electrical discharge machining.
The wire electrical discharge machine comprises a mounting surface plate 5 for mounting the workpiece 3 thereon; a processing tank 7 for keeping the workpiece 3 and the mounting surface plate 5 immersed in a working fluid 60a; a guide means 8 for guiding the wire electrode 1; a lower idler 20 for converting the direction of the wire electrode 1 being fed from a lower portion of the workpiece 3 into a horizontal direction; a wire conveying means 22 for conveying the wire electrode 1 and having a pipe-shaped portion; a wire taking-up means 30 for taking up the wire electrode 1; a cylinder 50 for moving the wire taking-up means 30 in the horizontal direction; a working-fluid supplying section 60 for supplying the working fluid 60a to the wire conveying means 22; and a collecting section 75 including a shielding plate 72 and a collecting box 74.
The wire conveying means 22 comprises a hollow cylindrical inlet portion 22a into which the wire electrode 1 is inserted and the working fluid 60a is allowed to flow from a side surface thereof; a hollow cylindrical guide member 23 connected to this inlet portion 22a; and a nozzle member 25 which envelops the guide member 23 and is formed slidably around an outer peripheral surface of the guide member 23 and which is larger than the guide member 23. As a rod 50a of the cylinder 50 is extended or retracted, the wire conveying means 22 moves the overall wire taking-up means 30 in the horizontal direction, and is adapted to allow the nozzle member 25 to be movable in synchronism therewith.
The wire taking-up means 30 includes a capstan roller 34 serving as a first roller for nipping and taking up the wire electrode 1, a lever-type pinch roller 36 serving as a second roller, and a motor 32 for rotating the capstan roller 34.
The working-fluid supplying section 60 includes a storage tank in which the working fluid 60a is stored, a first pump 64 for pumping up the working fluid 60a from the storage tank 62 and supplying it to the processing tank 7, and a second pump 66 for supplying the working fluid 60a to the wire conveying means 22 in a similar manner.
Referring to FIGS. 6 and 7, a description will be given of the operation of the wire electrical discharge machine constructed as described above. First, the wire electrode 1 is passed through a machining portion 3a of the workpiece 3, undergoes a change in its direction by the lower idler 20, and is inserted in the inlet portion 22a of the wire conveying means 22.
Next, the second pump 66 is started, and the working fluid 60a pumped up from the storage tank 62 passes through the interior of the wire conveying means 22. A conveying force is hence imparted to the wire electrode 1 by the flow of the working fluid 60a as shown in FIG. 6, so that the wire electrode 1 is automatically fed to the wire taking-up means 30 and automatically drops into the collecting box 74. This drop is detected by an unillustrated detector to stop the second pump 66.
Next, the cylinder 50 is driven to move the wire taking-up means 30 to a position above the collecting box 74 and stops as shown in FIG. 7, and electrical discharge machining is effected. At this time, the wire electrode 1 which is continuously fed to the machining portion 3a of the workpiece 3 is collected in the collecting box 74.
However, there has been a problem in that when, during electrical discharge machining, the working fluid 60a flows from the processing tank 7 to the capstan roller 34 through the lower idler 20 and the wire conveying means 22, and the working fluid 60a is attached to the capstan roller 34, the wire electrode 1 becomes liable to be entangled with the roller 34 due to the surface tension of the working fluid 60a.